In a four-wheel drive vehicle (4WD vehicle) and a rear-wheel drive vehicle (FR vehicle), a propeller shaft configured to transmit a rotational driving force from a transmission to a differential is used. Further, for the purpose of improving the safety at the time of vehicle collision, there has hitherto been provided a propeller shaft configured to absorb an axial displacement at the time of collision to release an impact force (Patent Literature 1 to Patent Literature 3).
As illustrated in FIG. 4, a propeller shaft disclosed in Patent Literature 1 includes a steel pipe shaft 1 and a driven shaft 3. The steel pipe shaft 1 is a driving shaft. The driven shaft 3 is coupled to the steel pipe shaft 1 through intermediation of a constant velocity universal joint 2.
The constant velocity universal joint 2 includes a cylindrical outer joint member 6, an inner joint member 8, a plurality of balls 9, and a cage 10. The outer joint member 6 has track grooves 5 formed in a radially inner surface thereof. The inner joint member 8 has track grooves 7 formed in a radially outer surface thereof. The plurality of balls 9 are interposed between the track grooves 5 of the outer joint member 6 and the track grooves 7 of the inner joint member 8 to transmit torque. The cage 10 is interposed between the radially inner surface of the outer joint member 6 and the radially outer surface of the inner joint member 8 to retain the balls 9.
An end portion of the steel pipe shaft 1 is fitted into the inner joint member 8. In this case, a male serration portion 16 is formed in the end portion of the shaft 1, and a female serration portion 17 is formed in a radially inner surface of the inner joint member 8. The male serration portion 16 and the female serration portion 17 are fitted to each other. Further, a stop ring 14 is mounted to a shaft protruding portion protruding from the inner joint member 8 toward a pipe member 11 side to prevent separation of the shaft 1.
The outer joint member 6 has an opening portion on a side opposite to the shaft side, and is coupled at the opening portion to the pipe member 11 provided adjacent to the outer joint member 6. A seal plate 12 is fitted on the opening portion side. Specifically, an annular step portion 13 is formed on the opening portion side, which is the side opposite to the shaft side, of the outer joint member 6, and the seal plate 12 is press-fitted and fixed to the step portion 13. Further, an opening portion of the outer joint member 6 on the shaft side is closed by a sealing structure S having a rubber boot 15.
At the time of collision of a vehicle or other accidents, when an impact load Z acts in an axial direction from the transmission side, a reverse reaction force W acts on the driven shaft 3 as a reaction to the impact load Z. The reaction causes an internal component (unit body including the inner joint member 8, the balls 9, and the cage 10) of the constant velocity universal joint to slide relative to the pipe member (companion flange) 11 toward the pipe member 11 side. As illustrated in FIG. 5, the rubber boot 15 is broken, and the internal component presses the seal plate 12 toward the pipe member 11 side. As a result, the seal plate 12 is separated from the step portion 13. With this action, the impact is once absorbed. Then, as illustrated in FIG. 6, further movement of the internal component of the constant velocity universal joint toward the pipe member 11 side is allowed, thereby being capable of absorbing the impact.
According to Patent Literature 2, a seal plate integrally including a metal core and rubber is provided. At the time of impact, the metal core is separated from the rubber at a rim portion so that the seal plate is allowed to enter the companion flange together with a joint internal component (component including an inner joint member, a cage, and balls).
According to Patent Literature 3, a seal plate integrally including a metal core and rubber is provided, and a through hole is formed at a center portion of the metal core. At the time of impact, the shaft breaks through the rubber and is allowed to enter a companion flange through the through hole of the metal core.
With regard to the related art, the following problem in terms of safety is conceivable. That is, the propeller shaft protrudes at the time of collision of the vehicle, with the result that a significant impact force may act on the vehicle, or the pipe portion may be buckled into a V-shape to enter a vehicle cabin. Therefore, in order to absorb the axial displacement which may occur at the time of collision, there has been proposed a mechanism which allows the internal member of the constant velocity joint to enter a hollow portion of the companion flange or the pipe portion.